1. Field of the Invention
This invention relates generally to a process for detecting an anode pressure sensor failure in a fuel cell system and, more particularly, to a process for determining maximum and minimum anode pressure sensor readings over a period of time to determine if a threshold difference between the minimum and maximum pressure has been achieved to determine if there is an anode pressure sensor stuck failure.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode to generate free hydrogen protons and electrons. The hydrogen protons pass through the electrolyte to the cathode. The hydrogen protons react with the oxygen and the electrons in the cathode to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer electrolyte proton conducting membrane, such as a perfluorosulfonic acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The catalytic mixture is deposited on opposing sides of the membrane. The combination of the anode catalytic mixture, the cathode catalytic mixture and the membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation.
Several fuel cells are typically combined in a fuel cell stack to generate the desired power. For example, a typical fuel cell stack for a vehicle may have two hundred or more stacked fuel cells. The fuel cell stack receives a cathode input gas, typically a flow of air forced through the stack by a compressor. Not all of the oxygen is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The fuel cell stack also receives an anode hydrogen input gas that flows into the anode side of the stack.
The fuel cell stack includes a series of bipolar plates positioned between the several MEAs in the stack, where the bipolar plates and the MEAs are positioned between two end plates. The bipolar plates include an anode side and a cathode side for adjacent fuel cells in the stack. Anode gas flow channels are provided on the anode side of the bipolar plates that allow the anode reactant gas to flow to the respective MEA. Cathode gas flow channels are provided on the cathode side of the bipolar plates that allow the cathode reactant gas to flow to the respective MEA. One end plate includes anode gas flow channels, and the other end plate includes cathode gas flow channels. The bipolar plates and end plates are made of a conductive material, such as stainless steel or a conductive composite. The end plates conduct the electricity generated by the fuel cells out of the stack. The bipolar plates also include flow channels through which a cooling fluid flows.
Pressure sensors are an important piece of hardware for engine control in the automotive industry in general. There are diagnostics that cover a map sensor and a fuel pressure sensor for an internal combustion engine, where the fuel pressure sensor reading is compared to an estimated/model value and a trigger is set when the model and the sensor differ by a calibrated value. In fuel cell systems, pressure sensors are used for pressure control, emission control, valve control, etc. If one of the pressure sensor failures in a fuel cell system is due to a pressure sensor that is stuck at a pressure reading, the sensor will provide a flat pressure reading value over time. The cause for the pressure sensor being stuck at a pressure reading may be for a variety of reasons, such as hardware damage, ice frozen around the sensor, etc. Therefore, it is crucial to have a robust diagnosis algorithm to detect when a sensor failure in a fuel cell system is due to the sensor being stuck.
As stated above, when a pressure sensor is stuck the pressure feedback is flat for a certain period of time. In a fuel cell system, anode pressure feedback from an anode pressure sensor is used in anode pressure control, anode valve control, fuel cell system exhaust emission control, etc. A flat pressure sensor reading caused by a pressure sensor stuck failure does not reflect the true behavior of the fuel cell system, which causes other algorithms to not work properly. For example, during start up of the fuel cell system, if the anode pressure set point is set to 200 kPa and the anode pressure sensor is stuck at a constant pressure reading of 100 kPa, a controller of the fuel cell system will keep sending a maximum duty cycle command to an anode fuel injector to try to meet the pressure set point of 200 kPa. This will cause the anode pressure to rise, possibly above 700 kPa. Since the pressure reading is still 100 kPa, the system is not reflecting the true anode pressure. Eventually a shutdown diagnostic may detect that there is an issue and shutdown the fuel cell system. However, there is a need in the art for an algorithm that determines when an anode pressure sensor is stuck such that remedial actions may be taken before a shutdown diagnostic is triggered.